Commit 3557f62e authored by Cong Wang's avatar Cong Wang Committed by Ben Hutchings

mqueue: fix a use-after-free in sys_mq_notify()

commit f991af3d upstream.

The retry logic for netlink_attachskb() inside sys_mq_notify()
is nasty and vulnerable:

1) The sock refcnt is already released when retry is needed
2) The fd is controllable by user-space because we already
   release the file refcnt

so we when retry but the fd has been just closed by user-space
during this small window, we end up calling netlink_detachskb()
on the error path which releases the sock again, later when
the user-space closes this socket a use-after-free could be
triggered.

Setting 'sock' to NULL here should be sufficient to fix it.
Reported-by: default avatarGeneBlue <geneblue.mail@gmail.com>
Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: stable@kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 1b31fcb2
......@@ -1095,8 +1095,10 @@ SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
timeo = MAX_SCHEDULE_TIMEOUT;
ret = netlink_attachskb(sock, nc, &timeo, NULL);
if (ret == 1)
if (ret == 1) {
sock = NULL;
goto retry;
}
if (ret) {
sock = NULL;
nc = NULL;
......
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